The diagram below show how sand dunes formed

The above diagram depicts the shape process of sand dunes. Overview, there were three steps which included four main factors: sand particles, wet ground, dry ground and wind direction.

In the first picture, the wind blew down the sand particles to the right side which had 4 objects drop into wet ground. Likewise, the wind direction in stage 2 was probably on the same side as the first one. With the help from the wind, there appeared more sand balls which were built for a foundation of sand dunes.

Last but not least, the third picture also was a final stage. A second arrow was upward which was the only one different from the rest. In this part, sand dunes were almost done, the shape is located in a wet place.